Is Mafia always this slow also?
There are typically slow periods in our mafia games (like weekends, when everyone is doing RL things), but I suspect part of what is hurting the pacing here is that there are lots of breaks while waiting for specific players to do things. The nature of Secret Hitler has a lot of short (in RL, anyway) breaks, but being global and asynchronous is going to expand each of those breaks quite a bit since you need to wait for 3 people to each take actions and those actions can't be done in parallel.
Mafia can move a little faster because mainly you just need a majority to vote in order to end a Day phase, which can be done in parallel, while Night phases only last about 48 hours or so anyway. If a specific player is stalled out for a RL day or so, the others can keep going (unless everyone is agreed to wait for the absent person).