Clothes washers are normally rated at 3 DFU each. Clothes washers in a battery of three or more are rated at 6 fixture units when sizing the common horizontal and vertical waste pipe sizing to take into account the possibility of simultaneous discharge and the suds producing effect in the drainage piping.
A 1&1/2 inch pipe is rated at 2 DFU vertical and 1 DFU horizontal.
A fixture unit is a numerical load factor which measures on some select scale the load-producing effects of a single plumbing fixture of a given kind.
It makes no difference whether a 1 1/2" line can drain the washer, because you are not going to get it approved until you satisfy the inspector. But, almost, if not all, codes do call for at least a 2" drain for a washer.