YES, delete them.
I still have some incredibly PB times for some combos, and people ask me how it is even possible. They were VERY early S2 PB times, and nearly 2-3 seconds faster than the World Record, haha.
That goes to show how long some of my PBs have been standing, and I've never really deleted any of them.
At least keep the amount of laps driven statistic, but delete the PBs please, it is always nice to start with a new/fresh set of times to aim for. Afterall, we do love to improve our PBs don't we?