My Brother in Law (Philadelphia, PA) is supposed to be getting divorced. (it's been close to 2 years, if not longer) How long can his wife drag this out?
It's been years. Pretty sure his lawyer is completely useless, but he doesn't want to find a new one because he has spent all this money.

There is no real or good answer to your question as there are so many variables.

Unless someone is contesting things, you can have a divorce done in well under 60 days.

Ironically my SIL is getting a divorce.  Her superdouche of a husband is doing everything to drag it out.
Its been almost 2 years now.  Now with covid and courts stalled shes even more fucked.

She needs to call that ACDC guy...

Is there a maximum time span, before he can just finalize the divorce without her fighting it?  She's being as difficult as possible, because she can.

Rarely is there a maximum time, but if there is one, it is governed by that state's law.  As mentioned, a variety of variables can draw things out, like custody battles, fights over assets (especially if they own a business), negotiations of a property settlement, etc.

Your brother should light a fire under his own lawyer's a@#.  Your brother can drive it towards closure, but he has to be active and not just wait for it to happen and allow her to drag things out.  Active management of his own case may cost more out of pocket now, but can get things moving faster.

Im my SIL's situation, you must wait 1 year from when you are officially separated.
Well getting to the starting point was difficult.  
She had to petition the court because there are certain prerequisites that need to happen to start the year.
He did everything he could to delay that start.
He requested  a jury be present.  That has to be scheduled.
The courts moved slow as shit before covid.  

This is all NC.  Do NOT get divorced in NC.  Its ass backwards and slow.

37 days here in FL start to finish. Joint stipulated with the final agreement after five days of back & forth haggle. Had to each participate in a parenting class that took 10 days or so. After that, had to wait on the clerk to file and calendar everything.

FL is cut & dry. Using lawyers means everyone suffers.

Kill all the lawyers.

My Marriage lasted a month under five years from the time we walked down the aisle till the time she had me served.

My divorce took a month over 7 years from the time she had me served till the day it was final

Custody\support is still dragging its way through the courts, 11 years on.