Bitlocker Performance Impact Windows 10

Of course.
BTW, it may be a good idea to add more RAM.
Late 486 boards with PCI usually have 4 x 72-pin SIMM sockets, so even 128 MB seems possible - though probably with only 64 MB cachable.
With 64 MB of RAM Windows 98SE might run pretty well even on a 486, and there are even good chances for Windows NT.