Aldo, I would disagree with that description.

15 requires the newly ROW boat to initially give the newly Keep Clear boat an opportunity and room to keep clear.  

So, if the KC boat can immediately alter course in a seamanlike way, meet her other obligations under Part 2 and 31 and keep clear, the ROW has given her that room.

If the maneuver requires the KC boat to crash tack  or gybe for instance, or break another rule relative to another boat or touch a mark, then that is not giving room to keep clear. 

PS … if I was explaining 15, I would immediately go to the definition of room and walk them through that.

Doing that for someone learning the rules has benefits beyond just 15, as it becomes the foundation for mark-room, 16, and other rules as well. 

If the other boat can immediately manoeuvre in a seaman like way then 15 is not broken. The give way boat is tasked to keep clear immediately 

To add to Michael’s comment, I’ve always read this as if the new give way boat can immediately keep clear, then the boat acquiring ROW has satisfied 15. The key is in the definition, meaning that the new give way boat not only has to be able to maneuver in a seaman like way, she has to be able to do so in a way that meets the definition of keep clear.

To illustrate, let’s look at the classic boat overtaking to leeward. A boat overtaking is give way up and until the moment she establishes an overlap to leeward. Once she does, because she established the overlap, she’s subject to 15. If at that moment the give way windward boat cannot maneuver without making contact (see the definition of keep clear, specifically (b) in the definition), then the boat acquiring ROW has broken 15.

Tom, I think your last line in your post is incorrect.  US Appeal 119 in the first half requires actual contact for the overtaking boat to be penalized under rule 15 not merely room to keep clear.  I think the rule now should be read as “room to avoid contact”.  In the appeal the appeal committee finds that the windward boat was unable and failed to keep clear, yet did not penalize the overtaking boat because there was no contact.  So studying the definition of “keep clear” is likely to lead one astray.  It would help if the rule was reworded, I think.

Bob, I don’t think the appeal suggests that at all. What the appeal does say is that the boat acquiring ROW bore away to give room for the newly give way boat to keep clear (required under 15). This is precisely the requirements laid out in 15. The appeal even goes so far as to note that while give way technically breaks 11, she would be exonerated because she’s sailing within the room she’s entitled to because of 15.

My comment, therefore is correct, but incomplete. ROW doesn’t break 15 if she gives room, but she would in my scenario if she either doesn’t or is unable to.

To summarize, the answer to the original question is "No".  If, after B becomes ROW, A needs to maneuver in order to keep clear, then she must do so immediately, as long as she can maneuver to keep clear without causing damage.  Full stop.  I think the additional remarks, about B's obligations, , contact, etc., are helpful in understanding the whole situation, but I want to make sure the original question is answered in an unambiguous way.  

Rob re: “then she must do so immediately, as long as she can maneuver to keep clear without causing damage.  Full stop.”

Though I agree the answer is “no” to the OP question, I really prefer my description better since 15 uses “room”. 

I don’t see “damage” as a criteria, but rather the keep clear boats ability to [maneuver in a seamline way and] meet her obligations under Part 2 and RRS 31 (which obviously includes RRS 14 as one aspect). 

To use the phrasing of the OP, if B does not allow A  to manoeuvre to keep clear after B obtained ROW, then B broke 15.   

Definitively agreeing with Angelo about not considering the damage, or even a contact, as a criteria.

Well, also thank for making me focus on the definition of "room" and  "keep clear". 

The word "keep" make (made)  me think this way: if i have to keep something, i must have it before hand. So my way of reading RRS 15 is (was) that A should give B a space equivalent to keep clear, and then B should "keep" that condition. 

Now you say A should leave only "room" to allow B to put herself in a "keep clear" condition. Right? So the discrimination would now be if the action of keeping clear was seamanlike.... difficult to ascertain.

At an old hearing, an IJ told me that A (that get a DSQ, notwithstanding B avoided contact and managed to keep clear) should have given to B at least 3 seconds, being that their usual standard to apply a RRS 15. What do you think?

Thank you all for your replies.

A good way to understand a rule or a definition is to read all the Cases that reference the rule.

Rule 15 ACQUIRING RIGHT OF WAY is referenced in 10 cases. 2, 7, 13, 24, 27, 53, 81, 93, 105, 117
As rule 15 uses the definitions room and keep clear you should also read cases that interpret those definitions.

Case 88, A boat may avoid contact and yet fail to keep clear, has a good discussion about keep clear and is worth reading.

In the case of the boat becoming overlapped to leeward:

L becomes RoW boat immediately, but is subject to rule 15.
W must respond promptly once the overlap is established, but is not required to anticipate.
If W does respond promptly but there is contact with L (or there is no contact but W is required to make an unseamanlike manoeuvre), then L has failed to give room and breaks rule 15.If W could have kept clear, but either respnds too slowly, or not enough, or over rotates and cause cntoact then W has broken rule 11.

If, for example, W has no steerage way, and cannot luff she may sheet in to accelerate. If in doing so, because fo the characteristis of hull and keel, she intially makes leeway and there is contact then L has not given enough room

Very nice gordon

Largely based on Call RS B1 in Radio Sailing Call Book.!

Match racing call MR B3 covers this too, as well as Case 24 (which the call references).

Well, thank you all.
Thanks to Mark, reminding me of the case book. Case 24, is very clear about "responding prontly". 
So that's it; so for the PC, in a hearing, should determine wether the prompt action taken by the boat that acts to keep clear, was, or was not, made in a seamanlike way. Tough.