A good quality 30wt is Briggs recommendation
White Outdoor LT2150 with 21HP OHV Briggs & Stratton
if it has one, it will be simple to remove the bolts and pull it off. if it doesnt, then you have to pull off one side of the crankcase.
30wt oil of any brand will work
If it an opposed twin, then an RJ19LM. If it is a V-Twin, then an RC12YC. Either gapped at 0.028 - 0.030"
30 weight non detergent.
Briggs 19.5 oil filter
Briggs and Stratton recommends SEA30 oil.
The 15.5 Briggs does not have an oil filter.
Briggs and Stratton is a select brand of lawn mower. When oiling one's Briggs and Stratton lawn mower engine, it is best to use a high quality oil. One can find such an oil at their local home improvement store, such as Home Depot.
Briggs and Stratton oil must be used for Briggs and Stratton engines. They have both synthetic and standard oil. They have oils formulated for 4-cycle and 2- cycle engines.
how to Change oil on a Briggs and Stratton 6.75 HP
Most Briggs engines that small take 1 pint of oil .