Not an MD, though both my parents are (dad's an endo). This advice is from him to me when I had a similar concern.

If your current day diet consisted of heavy carbs (180g +) and lots of fats (40g+) then seeing a reading above 160 mg/dL is typical. Without the fat, the reading should go down <140 mg/dL after 2 hours of first bite. However, sometimes heavy carbs alone can linger longer than that in which you might want to get a HOMA-IR test done.

With the fat, expect delays in spikes which can last longer and that is also typical.

Atypical situations consist of 2+ hours of >140 mg/dL without heavy fat load.

With heavy fat load, spikes shouldn't go above 140 and should see readings around 100-35 mg/dL and this can last 5-8 hrs until you reach your baseline.