@ftd ... you're only temporarily taxed that high. The process is kinda lazy - they take the paycheck amount x 26 and tax you at that rate from a table (as if you made that salary all year). But come tax time, you are reassessed on your real salary/bonus/dividends, etc. You likely will see a refund if you had planned your taxes to owe $0 before the PTO cash-out (or bonus paid).
If it were earlier in the year, you could always adjust your W-4 to take out less taxes on future paychecks to compensate. But since it's already October, it's not that long until you file taxes.
Just want OP to make an informed decision. As cited above, that money is yours and legally they have to pay it all out to you when you leave.