advices needed for MTB tyre covert to city tyre

[applio]

hi
i am thinking to change my 650b/27.5 MTB tyre to a city tyre for commute purpose, so do i need to get a new tube in order to fit the commute tyre？or the existing tube will do the job, as my current tyre/tube only take max 40 PSI, and the Tyre i am planning to swap is the Maxxis Detonator 27.5 x 1.5 (650B) MTB Tyre, which is max 80psi.
thank you for any advice.

[Duck!]

Pressure rating is irrelevant, the size is the critical thing. How wide are your current tyres? Any wider than 1.75" the tubes will be too difficult to fit into the narrower road tyres, so you'll need narrower tubes to suit.

[applio]

Pressure rating is irrelevant, the size is the critical thing. How wide are your current tyres? Any wider than 1.75" the tubes will be too difficult to fit into the narrower road tyres, so you'll need narrower tubes to suit.

the curent mt tyre on the bike is 27.5 x 2.10, and the tyre i am planning to get is 27.5 x 1.50

[Duck!]

You will need new tubes to suit the 1.5 tyres, as the 2.1s are too big.

[applio]

You will need new tubes to suit the 1.5 tyres, as the 2.1s are too big.

been search around the net, seems cant find a 1.5 tube, only fond 1.9 tube

[K2]

Maybe not relevant to 650Bs...but just for reference:

Ive been using cheap 26 x 1.5 Bikecorp/VeeRubber City Slick copies on my regular sized mtb for the last couple of years. Still using cheap tubes that are meant to fit 1.75/2.25 and 1.75/2.5 without problems. Originally had them for 2.0 knobbies and hate waste. As usual, I just put a little air in before fitting. I figure less stretching must put them in the "thorn resistant" class.

Tyres say 40psi. I now run around 70 rear and 45-50 front, again without anything untoward occurring. I crept up to those figures as I was a little wary at first.