Pasting data from Excel table takes very long I use SQL Server Management Studio 2012 to import data from Excel sheet to a table on SQL Server. I use the most straightforward way that I just Ctrl+C a table in Excel and Ctrl+V in table edit window in SSMS. I know that many other ways faster exist to import data. But this is most simple without a need to write any code.

But it takes 300 rows with 5 columns about 5 minutes. Is there any way how to speed it up without using completely different way that would require copying CSV on server or writing a script? Why does it take so long?
You don't need to write code. Just use the Data Import/Export Wizard.

Right-click on the database in SSMS, go to Tasks and Import Data. Select Flat File Source as your data source (because you're using CSV), and then browse for the file. Click next, select the database and the target table. You'll need to check the mappings for the CSV columns to the table columns (making sure the CSV column headings are the same as the table columns helps with this), and you can preview the data to make sure.

If everything is correct, click Next, Next and Finish to import the data. If there's an error, it'll tell you what it is (sometimes slightly cryptic though).

As a note though: I'd advise against trying to copy/paste/edit data in the Table Edit window. Writing SQL statements is a much more effective and time efficient way of doing it (or using the Data Import/Export Wizards).