Thailand + Japan?

Does it seem like too much to do Japan & Thailand for a 15 day honeymoon?

Was originally thinking only Thailand, and hitting north & south, but now leaning towards avoiding the North because of burning season.

It would be something like:
– Fly into Tokyo (days 1-3)
– Bullet train to Osaka, day trips if we have time (days 4-6)
– Fly from Osaka to stay in BKK (1 day trip to Erawan) (days 7-10)
– BKK to Koh Samui & Koh Tao for days 10-15

Does this seem like too much? Or is there another country you'd recommend that would make sense?

Thanks!