Is the 1500 custom truffles the contents of the 150 luxury boxes, or in addition? Molded, hand dipped, or rolled in cocoa?
If you have nothing else to do, 10 days might be possible. If you have molds that make 30 pieces and can make 10 at a time, that's 5 batches, that's do-able. A couple days of truffle production, a couple days to do the rest, a couple days to package. Assuming you can get all the packaging and ingredients in a timely manner.
I don't keep a ton of inventory, usually only 2-3 dozen of any one item. If I got an order like that right now ... I'd probably try to take it on because April is otherwise really slow, but it would take way longer than I want it to because these thing always do and there would be late nights when I questioned my life choices. Ideally I'd want confirmation 2 weeks in advance for an order like that, they are cutting it close especially since you have to ship it.