Do I get the impression I am doing homework?
Anyway ahh the ambiguity of numbers and the English language and that is before we consider long vs short scale though at the million mark it is still the same (without doing a search I am not sure what the Czech Republic uses but I am willing to bet it is the long scale where most of the English and Arabic speaking world it is now the short scale).
In speech at least you could be forgiven for assuming they are all the same and that would be 1500000, indeed anybody trying to say otherwise would probably be trying to mislead you.
In text you would hopefully have more context. That said when dealing with numbers around a million or a few hundred thousand the half does not matter (see significant figures) so most of the time in general discussion it would be ignored and you can then assume it is 1500000 (maths, science, engineering and accounting/finance are different matters so ask in those cases).
"One and half million" - most of the time in English that would be "one and a half million" which is to say a million and half that again. Equally the lack of the word "a" in various points there or the lack of a comma to do a similar job is quite jarring to most native English speakers.
On commas- much of the English speaking world (and a few other places besides) was historically seen to use them to separate numbers, a lot of places are trying to do away with the comma as a number separator (I was discouraged from using them and tend not to) though, as you have probably used as comma as a decimal point/decimal mark your entire life sticking a comma in numbers like 1,000,000 will look quite odd to you but this is probably a different discussion. When numbers are spelled in words it is different and you would do well to use commas appropriately.
If you were going to say one million and a single half (0.5) most would probably make it certain by saying "one million point five" though a switch of the word order leads a somewhat more common phrase (one point five million means 1500000) so be careful there.