Since I homebrew monsters with some regularity, I've found that how quick a fight goes in 5e tends to be more a function of how the enemies are statted out than anything else. Challenge rating, used indirectly to balance an encounter, is simply the average of an offensive CR and a defensive CR. This means you can make a creature stronger either by letting it spam Fireball (3) over and over, or by cranking its HP and AC up really high. I've found that high-defense fights tend to be the long, plodding ones, since most turns are either the PC missing, or when they do hit, taking off something like 5% of the enemy's HP. It's even worse if your players are all tanked up too and/or the enemies have no reason to target the squishy casters in particular. As a result, I try to tune for lower-defense enemies, then balancing it out by either giving them more of them to fight (which makes action economy more important), or if it makes sense to the story, triggering multiple encounters per adventuring day (which makes resource management more important and short rests become relevant).
The nice thing about being a wizard is you have lots of utility spells you can sometimes use to avoid combat altogether.
