Another tip for sewing on heavy fabrics is to use adding machine tape on top of and underneath your fabric. It can help the machine feed the fabric through the feeddogs. You can also use strips of tissue paper (the type used in wrapping gifts, not the bathroom type). The stitching will pierce the paper and you just rip it out after stitching. Any paper remaining will not affect the seam.
If your machine has a presser foot pressure adjustment, try adjusting it up or down to see if that helps.
Could I use a Japanese paper for that? So i could still see the lines I'm following for the stitches..