Is there an easy formula for multiple saving throws?

My issue: I am playing a druid and if I do something like summon 8 wolves I can end up forcing the DM into 8 saving throws each turn.

I mitigate this on my end with an app to roll lots of dice, I pre-roll my attacks and damage and all that, so my turns are quick, but the DM mentioned after the game that he doesn’t like having to roll so many saving throws, and worries it might slow things down.

Is there a reasonably simple formula to convert multiple saving throws into a single dice roll?

Example: 8 DC12 Strength saving throws becomes a single DC18 save – the outcome being that the target has a similar % chance of overall success, but with less dice.

My expectation is that given there are various throws of various difficulty, and each creature will have a different bonus that what I am asking for simply can’t be done, but I don’t have the maths to prove that.

What I am not looking for are ways to convince the DM that it isn’t too bad (It is no different than a well placed AoE for example), or to not summon so many wolves, spread the attacks around, or that I don’t get to pick what I summon, or any of the other usual advice about saving table time. My turns take seconds because I plan in advance, and I don’t think the DM wants to change what they do (IE: no using a dice roller for them), so this is just me looking to answer this one question.