To decrease the stitch count for the linked treble crochet stitch, you will need to stitch 2 linked treble crochets together.
To complete a linked treble crochet two together:
Pull up loops in first & second horizontal bars from the ltr stitch you just made and pull up loops in the next 2 stitches (5 loops on hook).
Yarn over and pull through the first 3 loops on your hook, yarn over and pull through next 2 loops, yarn over and pull through last 2 loops.