Also, there seem to be only caracterization data for 1.2V. Will they work at 1.5V ? Or should that be avoided ?

The

mosfets

are qualified for 1,5 V so it will work, the issue is the performance details estimation since you do not have liberty file.

Sure, I know the fets won't die, but given that sram is a delicate balance of one fet overpowering another, it didn't seem ou tof the question for me that a different supply could mean the balance is off and the sram non-functional at all.

usually overdriving SRAM is fine: undervolting SRAM might get some bitcells fail due to poor write margin or poor read margin