Help understanding withholding rate for Mexican resident for US bank account

I am helping a friend with opening up a personal US bank account. The friend is currently a resident of Mexico (does not meet substantial presence test for US). They are both a UK and Mexican citizen. As part of opening the account the bank they need to file the W-8BEN form. I am having trouble understanding what should be put for Part 2, line 10 for the withholding rate. There is. Mexico-US tax treaty but I am having trouble understanding which applies to this. We are looking to open a checking and savings account, which would mean the only applicable income should be interest income. I believe the applicable part from the tax treaty at https://www.irs.gov/pub/irs-trty/mexico.pdf would be article 11, paragraph 2, section C, which would be 15%. Is that correct?