can't help you with settings for your printer, but i also have problem understanding your exact issue.
for example, what part you consider unsuccessful:
- you tried to print 15 times and nothing happened (no drivers installed, paper jams, out of toner, ...)
- you tried 15 times and print coverage was light or uneven (printing works but print does not look ok)
- you printed 15 times, print was ok on paper but your toner transfer to PCB was not ok (it was light or inconsistent and needed lot of patching or etching ate through toner)
Toner is plastic and in order for it to work in toner transfer method commonly used to prototype PCBs it needs to melt at the right temperature and stick to copper clad board. Not all toners are equal. Quick google search using your printer name and "pcb toner transfer" returned this link:
https://www.instructables.com/id/Toner-transfer-no-soak-high-quality-double-sided/
one of the replies in that page is that toner transfer may not work on Brother because of used toner. This may be something to investigate. Another post on same page suggests that using same printer laminator produced perfect results first time...
It is hard to offer help when there is not much to go on. why don't you post some pictures of your troublesome prints or etching attempts?