@Teknor I tend to agree something is wrong, but I think it really on depends how many nodes and how often you're sending data.
rpi3 + GPIO nrf24l01 + openhab2 + 8 nodes + packet received, on average 1 / 5s :
top - 06:29:37 up 2 days, 22:33, 2 users, load average: 0.26, 0.24, 0.19
KiB Mem: 947732 total, 903420 used, 44312 free, 175364 buffers
KiB Swap: 102396 total, 4496 used, 97900 free. 391360 cached Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
681 root 20 0 208840 56532 23684 S 8.9 6.0 214:23.60 Xorg
527 root 20 0 39448 21532 11264 S 4.3 2.3 69:34.28 vncserver-x11-c
1154 pi 20 0 50548 17628 12196 S 3.0 1.9 64:05.96 lxterminal
30426 openhab 20 0 441764 197592 14960 S 1.6 20.8 284:18.70 java
2467 root 20 0 20024 2456 2300 S 1.3 0.3 62:55.17 mysgw
25634 root 20 0 0 0 0 S 1.0 0.0 0:00.21 kworker/u8:0
688 root 20 0 13720 9432 8828 S 0.7 1.0 2:04.96 vncagent
25855 pi 20 0 5232 2584 2140 R 0.7 0.3 0:00.49 top
7 root 20 0 0 0 0 S 0.3 0.0 9:15.35 rcu_sched
78 root -51 0 0 0 0 S 0.3 0.0 5:16.50 irq/92-mmc1
967 pi 20 0 95656 17716 12028 S 0.3 1.9 6:41.87 lxpanel
1 root 20 0 24620 4688 2716 S 0.0 0.5 0:13.08 systemd
2 root 20 0 0 0 0 S 0.0 0.0 0:00.27 kthreadd