For a 7 GB database 1 1/2 hour export time doesn't seem very long to me. Make notice that the writing of the ASCII files only takes a considerable amount of time. That's why different utilities are developed for backup; the backups are stored in IDS specific format and not readable for other purposes.
dbexport is a single threaded utility, will only use 1 CPU. dbimport is even slower as the indexes will be rebuilt.
ontape can be used for backup .. DB is only 7 GB so this will work fine
onarchive is no longer supported.