Just having good tires is all you need.

I would also suggest riding 'IN' your SD as it is much safer this way.

I would argue that there is no way that swapping from 14s to 15s will make it easier to get over 65. Just doesnt make sense.

__________________
85 300D 3 pedal. Current project.
83 300TD (need rear wiper assembly dead or alive)
84 300SD Daily driver
85 300TD almost 400k miles and driven daily.
98 E300D *sold
86 300SDL *sold and made flawless 10 hour journey to new home.