Is it right to write "1.5 meters" and "0.5 meter"?

First about the spelling.
English spelling of the unit of length is metre and not meter. In English vocabulary, meter means the instrument that measures. In American English, there is one spelling for both and that is "meter".

Next, about using the plural form.
According to the grammar, plural for meters is used for 1.5 meters, just as feet is used as a plural form of foot. However, in scientific terminology, plural form "meters" is not allowed according to SI system of units as it may mean product of meter with seconds (s means seconds). Hence only singular form "meter" is allowed in scientific SI system of units.

EDIT:
Refer to the following link which clarifies that the plural form is not to be used. Read under the heading, "Writing unit symbols and the values of quantities". It is stated in it that "Symbols of units are not pluralised; e.g., "25 kg", not "25 kgs".

For the explanation from the viewpoint of language, refer to the second link.

Yes. 1.5 is a plural, more than one meter. 0.5 being 1/2 of 1 meter .

both need to be pluralized. 1.5 meters is correct. .5 meter is not. .5 meters, with the s is correct.

It is right to write 1.5 meters and 0.5 meter

1.5 meters = 4.92 feet
0.5 metres = 1.64 feet

yes. Measuring 1.5 meters you need more than one meter length, while measuring length of less than a meter, you need only one meter.

Yes, it is OK.

Meter Or Meters