Since you are not an every day player you might as well enjoy the R15 on those days you visit here, if you have the credits. Certainly having a CDP bonus that moves you to higher levels faster might be a positive reason to wait, but it takes a long period of time to reach 96 and the Bertha. There is the slower, weaker Max at 91but it is not as impressive as the R15. It's Christmas time, treat yourself!