You should absolutely contact the accountant prior to making any change and request clarification.
No one can tell you the accountant's rationale for the recovery period other than the accountant (although it does sound incorrect for a single-family home in this country).
If you do need to change to the standard 27.5-year recovery period, you will have to file Form 3115 and make a 481(a) adjustment and the form is not really suitable for preparation by inexperienced filers.
See https://www.irs.gov/instructions/i3115#idm140516453720416
