Spring itself started supporting Hibernate 5 only from Spring v4.2.
So Spring 3 + Hibernate 5 is an untested, unsupported and likely incompatible combination of versions.
Worst case, you may end up wasting time trying to solve tons of vague errors due to such incompatibility.
I think you should consider migrating to latest Spring 4.2 too. What features of Hibernate 5 are you interested in?