I'm sure the 3B can handle it as it's not a hardware limitation. Perhaps changing Pi-hole's own logging to Anonymous (Settings > Privacy) will help slightly so it's not logging all these lookups. Give Unbound a try and see how it plays. You can also change the 150 limit but I'd suggest only doing that if you are running Unbound, since you don't want to swamp upstream servers or risk hitting their rate-limiting or worse being blacklisted.