Before answering your question, let me point out something very important to know about Mark 16:9-20.  Most scholars believe that it is quite likely this passage was not in the original book of Mark.  This is one of just three or four passages in our Greek New Testament text which is questionable (including 1 John 5:7-8, Acts 8:36 and John 8:1-11).  In each case, the reading is not found in most of the highly reliable early manuscripts.  The discussion of which manuscripts contain which reading and which are most important to scholars in determining the correct original Greek text would require a long discussion.  I suggest you get a copy of my book "Reasons for Belief," in which textual variants are discussed (www.ipibooks.com).  Also, any good commentary on Mark will discuss Mark 16:9-20 in detail.

Because of the preceeding paragraph, the answer to your question may just possibly take on less significance for you.

About your question, I am not sure exactly what you mean "Mark 16:17-18 is for the apostles."  First of all, the writer of this passage (be him Mark or someone else) says "Whoever….."  Given that Jesus says his statement applies to whoever believes and is baptized, clearly most everyone believe this passage applies to us.  As for Mark 16:17-18, it is said that certain miraculous signs "will accompany those who believe:"  First of all, it says nothing about these signs only being done by the apostles.  In fact, we know from several passages, that many Christians besides the apostles worked miraculous signs.  For example, Acts 8:4-8 has Phillip working miracles which fit generally into Mark 16:17-18.  For this reason, I really do not know what you mean that this passage is only for the apostles.  Perhaps what you really mean is that this passage only APPLIED to the apostolic age.  This is a possible interpretation.  In other words, one interpretation of Mark 16:17-18 is that when the message of belief and baptism for forgiveness is delivered to the world, this delivery will be accompanied with certain miracles.  There is good reason to believe that the miraculous gifts which accompanied the apostolic message were only given by laying on of apostolic hands.  Acts 8:9-23 seems to imply that only apostles had the ability to pass on the miraculous gifts.  Clearly no one today has had an apostle lay hands on them.  We have good evidence from the history of the early church that the miraculous gifts had all but disappeared by the early second century, which agrees with this interpretation.   If that is the case, then it is a reasonable interpretation of Mark 16:17-18 that it applied to the time immediately after the giving of the gospel message in the first century, whereas Mark 16:15-16 clearly applies to all people at all times and places.

hello Why some Christians belive Mark 16:15-16 is for us and Mark 16:17-18 is not for us but for Apostle?