What is a 1.5m double bed?

Do you really mean 1.5 cm? 1 cm is the width of your fingernail.
I think it probably said 1.5 m (for metres), which I would guess is the width of the bed. Sounds about standard for a hotel bed.

The conversion factor is 1 inch = 2.54 cm.

Double = 137x187cm, Queen = 153x203, King = 183x203

1.5 m is 58.5 inches, which is between a US Double (54") and a Queen (60")

... we shall go to the horse's mouth for a brief lecture on this... Pikolin is one of the biggest manufacturers of mattresses over here. Check out this post (use Google Translate!): http://www.pikolin.com/es/blog/medidas-de-un-colchon-cual-prefieres/ they've even included a graphic, LOL!

PS. Note that both Double (locally 135cm or 53") and Queen size (150cm or 59") are often locally referred as "matrimoni" (literally marriage). Also, note that sizes vary depending on the country, thus a Queen size for example, is not necessarily exactly the same everywhere.

In Germany, a standard double bed (Doppelbett) is 1.8 m (71") wide, closer to our king than to our queen. Our 54" wide double bed is called a French Bed.

Thanks Lee... my point exactly :)

For extra info, over here: King size is 180cm or 71" and Presidential King size is 200cm or 79". Don't you go looking for these two sizes in most hotels... you won't find them -except in the suites at the top hotels.

To have any stars from DEHOGA (German Hotel and Restaurant Assoc) the beds must be at least 1.8 meters wide (although it appears they can have a queen size bed, but they have to notify you prior to the beginning of the booking process).