Perf. degradation due to TIMESTAMP WITH TZ

[Yash]

We have an application that loads millions of records into a table.
Around 10 fields in this record are date fields. We perform the insert
using SQL*Loader in direct path mode. The loading takes a few hours.
Recently we had to convert the date columns to TIMESTAMP WITH
TIMEZONE(3). After doing the appropriate changes in the SQL*Loader
control file, when we performed a load, we experienced a performance
degradation of 50%.

Is the slowdown inherently due to the type of the column?
Can somebody provide any suggestions for reducing the slowdown?

Thanks
Yash