Comparing equivalent Scala and C# string-manipulation code - with Scala running much slower
There is no reason for Scala code to be slower than C#.
The different is probably the time that it take to the JVM to load.
To verify that I suggest you to write simple code in C#, Scala &amp; Java which just print "Hello World" and see the different.  My guess is that the Java &amp; Scala will take the same time while the C# will be faster.
Then just do something which do long calculations and see the different again.