ISR - High CPU with the process SNMP Engine

I have a Cisco 1841 router running in my lab, running code 15.0(1)M, experienced high CPU (9x% in most of the time) after I started to manage and monitor it via Prime Infrastructure 2.1.

When I do a "show process cpu | inc SNMP", it shows the SNMP engine is consuming 90 something percent CPU:

 309  2437791424     2302245     105531 92.36% 76.00% 74.82%   0 SNMP ENGINE    

And when I do a "show snmp stat oid", the mostly queried OID is ipNetToMediaEntry

time-stamp  #of times requested  OID

22:52:04 HKT Nov 20 2014 5261 ipNetToMediaEntry.1

22:52:04 HKT Nov 20 2014 5261 ipNetToMediaEntry.2

22:52:03 HKT Nov 20 2014 5261 ipNetToMediaEntry.4

22:52:03 HKT Nov 20 2014 5260 ipNetToMediaEntry.3

22:50:43 HKT Nov 20 2014 4100 sysUpTime

22:50:22 HKT Nov 20 2014 2 ciscoEnvMonMIBNotificationEnables.4

22:50:22 HKT Nov 20 2014 1 ciscoEnvMonMIBNotificationEnables.3

22:50:22 HKT Nov 20 2014 1 ciscoEnvMonMIBNotificationEnables.3

22:50:22 HKT Nov 20 2014 2 ciscoEnvMonMIBNotificationEnables.2

As a workaround, I have created a view to exclude ipNetToMediaEntry with the following commands:

DW-DESK-RT01(config)#snmp-server view cutdown iso included

DW-DESK-RT01(config)#snmp-server view cutdown ipNetToMediaEntry excluded

DW-DESK-RT01(config)#snmp-server community dshome view cutdown RW

And now it looks much better:

DW-DESK-RT01(config)#do sh proc cpu | inc SNMP

 156           0           6          0  0.00%  0.00%  0.00%   0 SNMP Timers      

 263           0           3          0  0.00%  0.00%  0.00%   0 EEM ED SNMP      

 264           0           2          0  0.00%  0.00%  0.00%   0 EEM ED SNMP Noti 

 267           0           3          0  0.00%  0.00%  0.00%   0 EEM ED SNMP Obje 

 307  1366776000     2507583        545  0.00%  0.00%  0.00%   0 IP SNMP          

 309  2887259424     2304177     105638  0.00% 47.55% 68.40%   0 SNMP ENGINE      

 310        4000           2       2000  0.00%  0.00%  0.00%   0 IP SNMPV6        

 311           0           1          0  0.00%  0.00%  0.00%   0 SNMP ConfCopyPro 

 312           0           2          0  0.00%  0.00%  0.00%   0 SNMP Traps  

Probably I need to upgrade my IOS code for this legacy old box....