I am using JET wanboot to install T5120 Guest LDOMs, some how the Guest LDOMs takes about 20+ mins to download the miniroot (only 214M) from the jumpstart server. When I try to use wget and only takes about 10secs.
20 minutes is not that unusual, though hardly ideal. It'll never be as fast as wget because typically only a single core is used by the firmware at this stage. There are bugs such as 6969316 that report issues like this; it's surmised that using a network interface other than e1000g to back the virtual device improves things, so you might try that if it applies to your situation.