Plug in the amp and be careful. Listen to the speakers. If they are farting out, you give 'em too much power. Or open the back and look at the Speakers. Should be easy to calculate the load. The wattage should be printed on the speakers as well.
If there are 16 Ohm loads, all wired in parallel, the cab is 4 Ohm. If there are 32 Ohm loads, all wired in parallel, the cab is 8 Ohm. And so on. Be quite sure, that the load of the single 15'-speaker is the same than the load of the 410. But, please, take care and have a look. Or take a multimeter and check it out. If the multimeter says 5.5 to 6.5 Ohm, the cab is an 8 Ohm load. It it says about 3 Ohms, the cabs will have a 4 Ohm load.
I found a forum with a post about this subject. They say, that the cab is a 8 Ohm load. I believe them, but I highly recommend a close look to the back of the speakers or a check with the multimeter. Here is the link:
Music Man Amps Discussion Forum: 410 HD-150 speaker impedence
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Play more bass!
Don't ever tell a bass player he's too loud Sayeth the Lord.