You can try these. But for later readers, there is no guarantee that they will be there for long time.
I4 = gmtread("https://fct-gmt.ualg.pt/tmp/LC82040332015145LGN00_B4.TIF"):
I3 = gmtread("https://fct-gmt.ualg.pt/tmp/LC82040332015145LGN00_B3.TIF");
I2 = gmtread("https://fct-gmt.ualg.pt/tmp/LC82040332015145LGN00_B2.TIF");