You have no idea what you are on about if you think you NEED C++ for an exchange trading engine

A good Java/Scala programmer can produce something 10 faster than a poor C++ solution

At BEST you can expect a C++ solution to be 30% faster than a Java design from the same person (that is only because you have more influence on pipelining in C++), only the Java version can be developed 2-5x faster

Any highly optimal design will be SEVERAL ORDERS OF MAGNITUDE faster than SQL using modern techniques

But you are right in that using integer values can be significantly faster than float/double (which also have serious precision problems) and far far more efficient than BigDecimal

But its easy for us to heckle from the sidelines - well done on producing something