Lv 10 SP potion reconvers 1452 SP.
Anything above that you have is only worth if you are going to bonfire since SP regen is turned off with Summoning.
Consider this: All classes rely on SP potions from some point on, it’s not uncommon, going SPR can help you in the beginning but you will still rely on SP pots after some points and all your invested SPR will have gone to waste.
Learn how to control your SP so it doesn’t really end, turn TS off sometimes. Servant takes ~12 seconds to cast all 5 buffs, I take ~18 seconds to recover 100% of my SP while sitting so even if I just wait for the buffs I can save many potions already. Try to wait for Summoning’s CD to end before you turn TS off.
Also consider that potions are very cheap once you reach higher levels and your income gets much bigger. Keep only good skills to use, remember TS does (~1700 + 4 x INT ) * 2 damage every 2 seconds for 1% SP only, so most weak skills are not worth their SP cost when compared to TS.