Tax deduction of dental treatment

Just spent 15000 for crown at the dentist. Can that be deducted from taxes in May?

Maybe yes, if you choose itemized deductions.
It may be deducted from your income, not from your taxes, though.

The applicable deductions for a resident of the R.O.C. in filing his/her income tax returns of 2018

There are two options; basic deduction and itemized deduction.
For most cases, basic deduction is better. Saves time and hassles.
Beware of accented IRS call if u choose the latter.